2. (Field of the Invention)
This invention relates to an electronic control ignition system for internal combustion engines, which electrically determines an ignition timing in accordance with a running condition of the engine.
2. (Related Background Art)
In the conventional electronic control ignition system for internal combustion engines which electrically determines an ignition timing in accordance with a running condition of an engine, a rotational angle of a crank shaft is detected in an angle pulse by a rotational angle detecting device. Based on the detected rotational angle, an ignition timing or a time during which a current is being supplied to the primary side of an ignition coil (hereinafter called current charging time) is calculated. Accordingly, higher resolution of the rotation angle of a crank shaft results in a more precise control of the ignition timing of an internal combustion engine in accordance with a running condition thereof. Taking this fact into account, devices have been made in order to improve the resolution of the rotation angle.
In a rotation angle detector as one of such systems, slits corresponding to, e.g., crank angle are formed on the periphery of a disk, such that a slit is detected to determine an ignition timing. However a problem of this system is that a numerous amount of slits have to be formed on the disk in order to obtain high resolution. Taking into account the ability of machining such a disk, that of sensing the slits and the durability of such a disk, such disk is not practical.
A photoelectric rotation angle detector has also been proposed. In this detector, a rotary disk having a required number of through holes formed on the periphery is mounted on a crank shaft. Further, light emitting element and a light receiving element are disposed at opposite positions where both elements come into alignment with each other through a through hole so that, based on interruptions of the light from the light emitting element, a rotation angle of the crank shaft is calculated. In this system, in order to prohibit adjacent ones of the electric pulse signals corresponding to the rotation angles of the crank shaft from interferring with each other, it is necessary to make the interval between each through hole and its adjacent one large to some extent. The disk has to be accordingly large sized and resultantly the rotation angle detector becomes large.
In addition, there is a system in which a reference angular position is changed selectively in accordance with the value of a calculated ignition lead angle (Japanese Patent Laid Open Publication No. 9656/1981).
In this system, an ignition lead angle indicative of an optimum ignition timing for a running condition of an internal combustion engine is calculated. Then, based on the calculated ignition lead angle, an ignition timing data indicative of a period of time from a time when the crank shaft of the engine has reached a reference angular position to an optimum ignition timing is calculated. Subsequently, when an instruction of an ignition timing of the engine is supplied, based on the calculated ignition lead angle, the reference angular position is selectively changed. In this system as well, a plurality of projections are provided on a disk, spaced from each other by 30.degree., and a projection is detected by a magnetic pickup sensor. Accordingly this device has similar problems of the above described systems.
In addition, there is a system in which an angle signal indicative of an ignition timing is divided into an upper position and a lower position. The positions are calculated based on angle signals of a crank shaft having different frequencies to thereby determine an ignition timing. However, this system has problems in that in order to increase the frequencies of the angle signals of the crank shaft, a multiplying circuit having a complicated circuitry is necessary. Further, in order to increase a multiplier and to perform the control with high resolution, a high frequency emitting source is necessary, etc.